Flood walls are slim vertical walls that are placed around a structure, property, or portion of a city to protect the surrounded area from flooding. Concrete flood walls may be used to protect an area in which there is not room for the massive footprint of a dike or levee; flood walls are also sometimes constructed on top of existing dikes or levees for additional protection.
Conventional flood walls are typically constructed from concrete panels that are usually four to ten feet high and 25 feet wide. These concrete panels are installed end-to-end with a small gap between the ends of adjacent panels, to allow for thermal expansion. This gap is filled with an expansion joint, such as a hollow rubber strip. The panels are fixed into the ground in some manner.
One type of conventional flood wall is called the “I-type.” The “I” refers to the shape of the wall's cross-section. The wall is generally slender in cross-section, possibly with a thicker section near the bottom. A sheet-like piling is embedded within each panel to fix the panels into the underlying earth.
To build an I-type flood wall (also called “I-wall”), the sheet pilings are first driven into the ground in a line. Concrete sheathing is cast in place over the pilings in sections, with narrow gaps between the sections, so as to form panels. If the flood wall were cast as a continuous length of concrete, internal stress from thermal expansion and contraction would lead to eventual cracking of the concrete.
The narrow gaps between panel, are filled by expansion joints. These are typically a strip of resilient material that is compressed or stretched as needed. Each expansion joint is attached to the panels on either side of the gap.
It has been found, such as in the flooding of New Orleans following Hurricane Katrina, that I-type walls are prone to catastrophic failure when the pressure from flood water is greater or more sudden than designed for, or if the water level overtops the flood wall and creates fluctuating forces as the water surges. Experience has shown that the concrete panels can deflect sufficiently to open up the expansion joints, allowing water to pour through. The mass of water spreads the gap and deflects the panel even further until the panel topples. Once one panel fails, it is wrenched out of place and starts a cascade of catastrophic failure along the flood wall.
Another reason for failure of I-type walls is if a portion of the soil supporting the I-type wall is too soft. The panels anchored in the soft soil tend to rotate away from the weight of flood water, opening a gap at the base of the I-type wall. Water enters the gap, further softening and scouring into the soil. This mechanism also leads to cascading failure of the flood wall.
Many of these I-type flood walls exist, because they appeared to be a cost-effective way to protect an area. Now that they have been shown to be less effective than expected, many cities and states are faced with expensive replacement, shoring up, or strengthening of their existing flood walls.
Another style of flood wall is called “T-type” because its cross-section resembles either an inverted letter “T” or an upright “L.” The horizontal bar is buried beneath the supporting soil and helps the panels of the wall resist rotation away from the force of flood waters. T-type walls are stronger than I-type walls, but can still fail in similar ways under sufficient forces.
There is a great need for a relatively inexpensive and simple means to reinforce existing flood walls. Because flood walls were often chosen as the preferred means of flood protection due to limited space, there is a need for a reinforcement system that does not require extensive excavation to install on an existing wall and that does not greatly increase the footprint of the flood wall. There is a need for a reinforcement system and method that addresses the known failure mechanisms of flood walls and strengthens the existing I-type wall to equal other, more robust, types of flood walls.
Preferably, a reinforcement system should be fast and easy to install to avoid undue disturbance to residents or businesses in the area.